Investigation of the influence of shot peening on stress corrosion cracking of stainless steel welded joints

High residual tensile stress is an important factor contributing to stress corrosion cracking (SCC). Shot peening can impose compressive stresses on the surface of welded joints that negate the tensile stresses to enhance the SCC resistance of welded joints. In the present work, the distribution of residual stress caused by welding is measured by X-ray diffraction method. The maximum stress in the weld is close to the yield strength of AISI 304 stainless steel, and the stresses are negative at both ends of the weld and far from the weld. The X-ray method is also used to measure stress caused by shot-peening. The results show that the higher the peening coverage, the higher the residual compressive stresses in the surface of weldments. While under the same condition, the residual compressive stresses induced by glass beads shot-peening are larger than those by cast steel shots. Temperature and stress fields of welding are simulated by using ABAQUS codes. The 3-D solid elements are used in FEM. Temperature depending on material properties as well as the convection and radiation as boundary conditions are considered. The 3-D linear reduced-integration elements are used to simulate the shot peening process. The results of simulation have a good agreement with experimental data. All unpeened and peened weldments are immersed in boiling 42% magnesium chloride solution during SCC test. Unpeened specimens crack after immersion for 6 hours. The steel-peened specimens with 50% coverage crack after 310 hours, while the steel-peened specimens with 100% coverage crack for 3500 hours. However, steel-peened specimens with 200% coverage and glass-peened specimens with 50%, 100% and 200% coverage are tested for a total of 3500 hours without visible stress corrosion cracks in the peened surfaces. The experiment results indicate that shot peening is an effective method for protecting weldments against SCC and weldments peened by glass beads resist SCC better than those peened by steel shots.